I did the hard mode russia because I'm retarded.
But it's actually not that hard, I had main character as my carry, but I'd imagine anyone with decent defense and good AoE can do. The key is Orichalcon, which you get from Atlantis.
Set it on your carry, and take 0 damage from normal attacks, and push through the winter
It gets harder on Moscow since all the field on your side has stat down and one of the spear unit had the defense piercing move, but what I did was bait the bombardment into row where Himiko isn't and just have some other unit to eat damage, but only Himiko and MC should survive by the end. Have Himiko heal MC from 1 space away until you take Ivan out, which you should be able to do with 1 Kagutsuchi. Once Ivan is out, you can move Himiko closer to MC to heal him better, and you should be able to outheal the defense piercing move from the NPC.